Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon

Definitions

• the present invention is concerned with an alloy structure essentially devoid of sigma phase which is not subjected to cold work and which, at room temperature, exhibits a 0.2% offset yield strength of at least about 517 MPa and, advantageously, at least about 689 MPa.
• An alloy disclosed in EP-A-0 052 941 and sold commercially is generally heat treated after solutioning and cold working by aging the alloy at about 732-733°C for 1 to about 24 hours, furnace cooling the cold worked and aged alloy to about 621-622°C, holding at that temperature for about 8 hours and then cooling in air.
• This procedure results in alloy objects, structures and the like which are adapted to be employed under high stress in sour gas oil well environments without danger of stress corrosion cracking.
• the solution treated cold worked and aged alloy generally exhibits a 0.2% offset Yield Strength at room temperature of at least 689 MPa.
• the problem is to provide large section alloy bodies, e.g., valve bodies, tube hangers, drill collars, various other items of oil well tooling, etc., which are not cold worked after solution treatment, which are aged to a 0.2% offset Yield Strength at room temperature of at least 517 MPa and which are resistant to stress corrosion cracking.
• alloy bodies e.g., valve bodies, tube hangers, drill collars, various other items of oil well tooling, etc.
• other mechanical characteristics of engineering significance of the commercial alloy such as Ultimate Tensile Strength, ductility, impact resistance, etc. should not be detrimentally affected by whatever means are employed to provide a solution to the problem.
• the alloy body should be free from detrimental phases such as sigma phase.
• the present invention contemplates an alloy structure in the condition resulting from solution annealing and aging, without cold working intervening, said structure being made from an alloy containing, comprising or consisting essentially of (in percent by weight) about 38-46% nickel, about 19-24% chromium, about 2-4% molybdenum, about 1.5% to 3% or 3.5% copper, about 1-2.3% titanium, about 0.1-0.6% aluminium, the sum of the aluminium and titanium contents being about 1.5-2.8%, up to about 3.5% niobium, up to 0.15% carbon, up to 0.1% nitrogen, the balance being essentially all iron.
• the alloy can also contain up to about 5% cobalt, up to 0.5% silicon, up to 1% manganese and residual amounts of melt additions such as boron.
• the structure is solution treated in the range of greater than 955° and up to 1100°C, e.g. 960° to 1100°C, and then aged for at least about 8 hours, e.g. about 8 to 30 hours of temperature above about 700° and up to 725°C, e.g. about 700 to about 720°C, for a time sufficient to induce in the structure a room temperature 0.2% offset Yield Strength of at least 517 MPa and, advantageously, at least about 689 MPa.
• the aging is at 700-720°C and is followed by furnace cooling to about 620-625°C and holding at that temperature for about 4 to 12 hours followed by air cooling.
• Alloy objects of the present invention advantageously have compositions within the range and substantially the specific alloy composition in weight percent set forth in Table I.
• the specific alloy set forth in Table I was cast and hot rolled to a flat having cross-sectional dimensions of 15 x 100 mm. Specimens were cut having long tranverse orientation and were annealed at 1010°C for one hour and water quenched. Tensile test specimens were 9 mm diameter and 35.6 mm long.
• Room temperature tensile test results are set forth in Table II based upon specimens which were isothermally aged at the temperatures and times indicated, followed by air cooling. Charpy V Notch test results are also given for the alloy resulting from the various test conditions. Table II shows that, with respect to room temperature mechanical characteristics of the heat treated alloy, there is little to choose between heat treatments A through F outside the present invention and heat treatments 1 to 3 within the invention with the possible exception that, a Yield Strengths above about 550 MPa, aging at 732°C produces alloy articles somewhat lower in Charpy Impact Value than articles aged to equivalent strength at 704°C.
• Table III sets forth data obtained in slow strain rate tensile tests conducted at 204°C in an autoclave with specimens immersed in an aqueous medium containing 20% sodium chloride, 0.5% acetic acid (glacial) and pressurized with 0.83 MPa gage hydrogen sulfide.
• Table II specimens 3.5 mm diameter 25 mm long were strained at a constant rate of 4 x 10 ⁇ 6S ⁇ 1.
• Table III clearly shows a distinct difference engendered in non-cold worked alloy objects by a small difference in aging temperature which is the discovery forming the basis of the present invention.
• More preferred heat treatments in accordance with the present invention comprise holding the alloy object solution annealed above 955°C at a temperature above about 704°C up to 725°C and for a time in excess of 8 hours e.g., 8 to 24 hours with longer times being employed at lower temperatures and vice versa.
• the alloy object can be air cooled, or, more advanta­geously, can be furnace cooled to about 621°C e.g., 610-650°C and held at that temperature for about 4 to 12 hours. Thereafter the alloy article is air cooled.
• Table IV sets forth two satisfactory heat treatments used on non-cold worked, solution treated alloy articles which provide alloy products resistant to stress corrosion cracking.
• alloy structures in accordance with the present invention have been made by conventional melting, casting and working operations.
• the alloy objects can be made by powder metallurgical methods wherein an alloy powder, perhaps made by atomization or by rapid solidification tech­nique or as blend of elemental or master alloy powders is compacted, for example, by hot isostatic pressing to form a near net shape alloy object.
• the alloy object can also be made by casting in any conventional or non-conventional manner.

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• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Organic Chemistry (AREA)
• Crystallography & Structural Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Physics & Mathematics (AREA)
• Metallurgy (AREA)
• Thermal Sciences (AREA)
• Heat Treatment Of Articles (AREA)
• Superconductors And Manufacturing Methods Therefor (AREA)
• Control Of Heat Treatment Processes (AREA)
• Powder Metallurgy (AREA)
• Heat Treatment Of Nonferrous Metals Or Alloys (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)

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Publications (2)

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• 1986
  • 1986-11-19 US US06/932,284 patent/US4750950A/en not_active Expired - Lifetime
• 1987
  • 1987-11-16 EP EP87116878A patent/EP0268241A3/de not_active Withdrawn
  • 1987-11-17 BR BR8706191A patent/BR8706191A/pt unknown
  • 1987-11-17 CA CA000551984A patent/CA1313110C/en not_active Expired - Fee Related
  • 1987-11-18 NO NO874804A patent/NO874804L/no unknown
  • 1987-11-18 JP JP62291671A patent/JPS63137135A/ja active Pending

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